1. Field of the Invention
The present invention relates to an antenna system, and more particularly to an integrated dual-band printed monopole antenna for WLAN (wireless local area network) application.
2. Description of the Related Art
With the prosperous development in wireless communications, the users also become very demanding in communication quality. It is required that the communication products be thinner, lighter, shorter and smaller, and stable communication quality is also a big concern. However, the multipath fading effect significantly reduces the communication quality of the system. Accordingly, it is necessary to employ antenna diversity to combat the multipath fading effect in wireless communication system.
Generally speaking, conventional antenna diversity can be accomplished in the form of frequency diversity, time diversity, or spatial diversity. In frequency diversity, the system switches between frequencies to combat multipath fading effect. In time diversity systems, the signal is transmitted or received at two different times to combat multipath fading effect. In spatial diversity systems, two or more antennas are placed at physically different locations to combat multipath fading effect.
U.S. Pat. No. 5,990,838, issued to Burns et al. on Nov. 23, 1999 entitled xe2x80x9cDual Orthogonal Monopole Antenna System,xe2x80x9d discloses a spatial diversity antenna system having a pair of monopole antennas respectively disposed on the top and bottom surfaces of the printed circuit board which has a first and a second dielectric layers, a conducting ground plane disposed between the first and second dielectric layers, wherein the pair of antennas are mutually orthogonal, and a feeding circuit is coupled to the pair of antennas for connecting to a principal system.
Although U.S. Pat. No. 5,990,838 has provided an antenna system of spatial diversity to improve the multipath fading effect in wireless communication system, the system can only be used in single-band operation and it fails to obtain optimal isolation between the two feeding ports of the antenna system (its S21 greater than xe2x88x9220 dB). Furthermore, U.S. Pat. No. 5,990,838 needs to use multilayer printed substrate, which requires a complex structure and high fabrication cost.
Therefore, it is necessary to provide an antenna system for effectively solving the problems of conventional art mentioned above, so as to be used in dual bands, e.g. 2.4 GHz and 5.2 GHz, wireless local area network, to obtain high isolation (S2 less than xe2x88x9220 dB) and to combat the multipath fading effect in wireless communication system.
It is a primary object of the present invention to provide an integrated dual-band printed monopole antenna which can be operated in dual bands for use in the 2.4 GHz and 5.2 GHz WLAN operation.
It is a another object of the present invention to provide an integrated dual-band printed monopole antenna having high isolation (S21) between the two feeding ports of the antenna to combat the multipath fading effect in wireless communication system.
It is still another object of the present invention to provide an integrated dual-band printed monopole antenna which has a simple structure and can be fabricated at lower cost.
In order to achieve the above objects, the present invention provides an integrated dual-band printed monopole antenna which comprises: a microwave substrate, a first dual-band monopole antenna, a second dual-band monopole antenna and a ground plane. The substrate has a first surface and a second surface.
The first and the second dual-band monopole antennas are disposed on the first surface of the substrate and are mutually orthogonal. Each of the first and the second dual-band monopole antennas is excited by a microstrip feeding line through a feeding port. The first and the second dual-band monopole antennas both include a first horizontal radiating metallic line, a second horizontal radiating metallic line and a vertical radiating metallic line. The first horizontal radiating metallic line is connected to one end of the vertical radiating metallic line opposite to the feeding port, the second horizontal radiating metallic line is connected to the vertical radiating metallic line at the position different from where the first horizontal radiating metallic line is connected to, and the other ends (free ends) of the two horizontal radiating metallic lines extend outwards in the same direction, whereby the antenna is formed as an F shape. For each of the first and the second dual-band monopole antennas, the path from the feeding port through the vertical radiating metallic line to the free end of the first horizontal radiating metallic line forms the first resonant path in operation and determines the first (the lower) operating frequency of the dual-band monopole antenna. In addition, the path from the feeding port through the vertical radiating metallic line to the free end of the second horizontal radiating metallic line forms the second resonant path in operation and determines the second (the higher) operating frequency of the antenna. Therefore, the antenna can be operated in dual bands.
The ground plane is disposed on the second surface of the substrate, wherein the ground plane has a main ground plane and a protruded ground plane extending between the first and the second antenna. The main metallic ground plane is rectangular or substantially rectangular shape, wherein two adjacent corners thereof are respectively cut off a 45xc2x0 edge portion, and the lengths of the two cut edge portions are the same. The first and the second monopole antennas are dispose respectively at an angle (xcex1) orthogonal (90xc2x0) to the edge of the main metallic ground plane and oriented symmetrically with respect to the protruded ground plane so as that the protruded metallic plane can effectively reduce the coupling between the two dual-band monopole antennas to obtain good isolation and impedance matching.